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From: Malcolm McLean <malcolm.arthur.mclean@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Running an editor from ANSI C
Date: Fri, 7 Jun 2024 13:57:25 +0100
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On 07/06/2024 10:37, Keith Thompson wrote:
> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>> On 06/06/2024 23:55, Keith Thompson wrote:
>>> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>>> On 06/06/2024 20:54, Keith Thompson wrote:
>>>>> David Brown <david.brown@hesbynett.no> writes:
>>>>>> On 06/06/2024 10:27, Malcolm McLean wrote:
>>>>>>> It does work. But my compiler warns about rmpnam() being deprecated.
>>>>>>
>>>>>> I presume you mean "tmpnam()" here.  No, it has not been deprecated -
>>>>>> not even in C23.  I could be wrong, but this sounds like one of MSVC's
>>>>>> arbitrary self-declared deprecations, using scare tactics to encourage
>>>>>> people to use MSVC's own functions rather than standard C functions,
>>>>>> thus locking you into their tools and platform.
>>>>> [...]
>>>>> You're right, tmpnam() is not deprecated either by ISO C or by
>>>>> POSIX.
>>>>> But tmpfile() is likely to be better for most purposes.  It creates
>>>>> a
>>>>> file and returns a FILE*.  tmpnam() returns a string pointer, and it's
>>>>> possible that some other process could create a file with the same name
>>>>> before the caller has a chance to create it.
>>>>> (mkstemp() is more flexible, but is not defined by ISO C.)
>>>>>
>>>> I want to run nano (or vi, or ed), in a shell running a pure ansi C
>>>> program. So the way to do it is to create a file, write the text you
>>>> want edit to it, them call system("nano readme.txt"). Nano then grabs
>>>> the  cobsole, which is what you want. You then read the file to get
>>>> the edited data.
>>>>
>>>> The shell isn't just a proof og concept. It has a practical purpose,
>>>> because it is FileSystem XML file editor. Whilst I'm playing about
>>>> putting Basic into it for fun, the real purpose is serious. And the
>>>> user must have an easy way of editing text files in the FileSystem
>>>> file.
>>>>
>>>> But it becomes effectively a virtual computer in its own right.
>>> OK -- but that has nothing at all to do with my post, which was
>>> about
>>> how to generate the temporary file name.
>>> One suggestion: rather than always using nano (which not everyone is
>>> familiar with), try reading the $EDITOR environment variable to
>>> determine what editor to use.  Concatenating the value of
>>> getenv("EDITOR"), followed by a space, followed by the file name, is
>>> likely to give you a valid command you can pass to system().  Fall back
>>> to nano if getenv("EDITOR") returns a null pointer.
>>> (For historical reasons, the convention is to use $VISUAL if it's
>>> set,
>>> otherwise $EDITOR if it's set, otherwise some default.  Originally
>>> $VISUAL typically referred to a full-screen editor like vi and $EDITOR
>>> to a line editor like ed, to be used when full-screen editing is not
>>> available.  That's unlikely to be relevant nowadays, and users typically
>>> either don't set $VISUAL or set it to the same thing as $EDITOR.)
>>> Don't do this for me; I'm not likely to use this.  But others are
>>> likely
>>> to find it more user-friendly if they can use a chosen editor.
>>
>> Ah thank you. But then main has to take an extra parameter. Now  will
>> the shell still be absolutely robust, and completely portable, and run
>> just anywhere?
> 
> What?  Why would main need an extra parameter?
> 
Hre's the main function for the shell.

int main(int argc, char **argv)
{
     char error[1024];
     char **list;
     int i;

     FILE *fp = 0;
     char *xmlstring = 0;
     BBX_FileSystem *bbx_fs_xml = 0;
     int err;

     if (argc < 2)
         usage();

     fp = fopen(argv[1], "r");
     if (!fp)
     {
         fprintf(stderr, "Can't open xml file\n");
         exit(EXIT_FAILURE);
     }
     xmlstring = fslurp(fp);
     if (!xmlstring)
     {
         fprintf(stderr, "Out of memory\n");
         exit(EXIT_FAILURE);
     }
     fclose(fp);
     fp = 0;

     bbx_fs_xml = bbx_filesystem();
     err = bbx_filesystem_set(bbx_fs_xml, xmlstring, BBX_FS_STRING);
     if (err)
     {
         fprintf(stderr, "Can't set up XML filessystem\n");
         exit(EXIT_FAILURE);
     }

     docommand(bbx_fs_xml, argc -1, argv + 1);

     fp = fopen(argv[1], "w");
     if (!fp)
     {
         fprintf(stderr, "Can't open xml file to write\n");
         exit(EXIT_FAILURE);
     }
     err = bbx_filesystem_dump(bbx_fs_xml, fp);
     if (err)
         fprintf(stderr, "Error writing FileSystem XML file to disk\n");
     fclose(fp);
     fp = 0;

     bbx_filesystem_kill(bbx_fs_xml);
     free(xmlstring);

     return 0;
}

Now to get the $EDITOR variable I will have to modify this function.

int main(int argc, char **argv, char **envp)

Now what are the implications of doing that? The point is that the shell 
is absolutely portable, because its filing system is stored as a single 
file on the host computer. And it mustn't break anwhere. I want David 
Brown to drop it into one of his embedded systems and see it work.

-- 
Check out Basic Algorithms and my other books:
https://www.lulu.com/spotlight/bgy1mm